7-hydroxycoumarin-based dyes (also called umbelliferones) and their derivatives are widely used as indicators for enzyme activity. One example of an umbelliferone is 4-methylumbelliferone (referred to as 4-MU), which is used for the detection of coliforms, amongst other things. The highest fluorescence of 4-MU (and other umbelliferones) is observed from the basic form, therefore such detection has to be undertaken at a pH of 8 to 10.